Chlorinated hydrocarbons such as 1,1,1-trichloroethane, other chlorinated solvents and chlorfluoro hydrocarbons (CFC's), such as C.sub.2 F.sub.3 Cl.sub.3, also known commercially under the trademark FREON.RTM., have been used for many years as solvents in numerous applications. These materials have shown to be very useful in the preparation of and as carriers for primer, activator, catalyst and accelerator compositions used in the adhesive field. These accelerators compositions often contain compounds, such as amine-bearing compounds, which require a solvent carrier for proper transport to and penetration of the substrate surface. Additionally, solvents are used to dilute the pure active compound to a useful concentration, usually on the order of about 0.01 to about 2% by weight.
In recent years, the use of chlorinated hydrocarbons, other chlorinated solvents and CFC's has been substantially lessened due to their deleterious effect on the environment. Regulations have been promulgated not only in the United States but in countries throughout the world to accelerate the phase-out of environmentally destructive solvents, and in particular those which are believed to be ozone-depleting substances. In addition to laws designed to prevent the use of these substances, product labelling requirements have also been promulgated to insure notice is given as to those compounds used as alternatives. Finding acceptable alternatives, however, has been an extremely difficult task. For example, in applications such as adhesive accelerator compositions, the solvent must possess high chemical stability, non-flammability, low toxicity, and have a low volatile organic solvent (VOC) content, yet be sufficiently volatile to readily evaporate once applied, depositing the active ingredient, e.g. an amine accelerator, on a substrate. In addition to these requirements, consideration must be given to cost factors which are important for commercial feasibility.
Attempts to find good solvent systems which balance non-ozone depleting and non-flammable characteristics with sufficient volatility to be useful in adhesive applications, have not been entirely successful. Although many materials possess the ability to act as volatile solvents, most have been too flammable or toxic to serve as suitable replacements for conventional ozone-depleting compounds, i.e. chlorinated hydrocarbons or CFC's. For example, materials such as heptane, acetone, methylethyl ketone, isopropanol, and methanol are excellent solvent systems, with good volatility, i.e. low flash point temperatures and high vapor pressures, but are extremely flammable. Other substances such as isoparaffins, and propylene glycol ether are less flammable, but do not exhibit adequate solvent performance properties for use in primer or accelerator compositions for adhesive systems.
One particular class of non-ozone depleting substances, which have been used in non-aqueous cleaning applications, are perfluorocarbons (PFC's). These materials are essentially non-toxic, non-flammable and thermally and hydrolitically stable alternatives to CFC's. In fact, the U.S. Environmental Protection Agency (EPA) has exempted PFC's from their VOC list, which indicates that they are non-ozone depleting and essentially non-reactive and non-polluting in the vapor phase. PFC's do, however, have the drawback of having low solvency for polar materials and most hydrocarbons. Thus, perfluorocarbons would not in themselves be expected to be useful as carriers for materials which require a solvent carrier, such as adhesion promoter compositions.
It is apparent, therefore, that a need exists for a solvent system which can carry actives, such as accelerator, activator, initiator, catalyst or primer compounds for adhesives, and which possess the following characteristics: non-ozone depleting, non-flammable, little or no VOC yet sufficient volatility for use as a carrier for active ingredients, low in toxicity and affordable in cost. The present invention is directed to overcoming the solvency deficiencies of perfluorocarbons, as well as addressing the aforementioned requirements for a useful alternative to CFC's.